U.S. patent application number 13/174396 was filed with the patent office on 2012-02-02 for power management system for wireless autonomous transducer solutions.
This patent application is currently assigned to Stichting IMEC Nederland. Invention is credited to Frank Bouwens, Guido Dolmans, Rene Elfrink, Li Huang, Valer Pop, Ruud Vullers.
Application Number | 20120030486 13/174396 |
Document ID | / |
Family ID | 43383395 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120030486 |
Kind Code |
A1 |
Pop; Valer ; et al. |
February 2, 2012 |
POWER MANAGEMENT SYSTEM FOR WIRELESS AUTONOMOUS TRANSDUCER
SOLUTIONS
Abstract
An autonomous transducer system is disclosed. In one aspect, the
system includes an energy scavenging module, energy storage module,
a load circuit having at least one functional block providing a
given functionality, and a power management module arranged for
providing power supplied by the energy scavenging module to the
load circuit or for exchanging power with the energy storage
module. The power management module may further include a tuning
module configured to tune the at least one functional block of the
load circuit according to a given configuration scheme.
Inventors: |
Pop; Valer; (Eindhoven,
NL) ; Bouwens; Frank; (Veldhoven, NL) ; Huang;
Li; (Eindhoven, NL) ; Dolmans; Guido; (Son en
Breugel, NL) ; Elfrink; Rene; (Waalre, NL) ;
Vullers; Ruud; (Waalre, NL) |
Assignee: |
Stichting IMEC Nederland
Eindhoven
NL
|
Family ID: |
43383395 |
Appl. No.: |
13/174396 |
Filed: |
June 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61361261 |
Jul 2, 2010 |
|
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Current U.S.
Class: |
713/320 ;
713/300; 713/340 |
Current CPC
Class: |
G01D 21/00 20130101 |
Class at
Publication: |
713/320 ;
713/300; 713/340 |
International
Class: |
G06F 1/32 20060101
G06F001/32; G06F 1/28 20060101 G06F001/28; G06F 1/26 20060101
G06F001/26 |
Claims
1. An autonomous transducer system comprising: an energy scavenging
module; an energy storage module; a load circuit comprising at
least one functional block providing a given functionality; and a
power management module configured to provide power supplied by the
energy scavenging module to the load circuit or to exchange power
with the energy storage module, wherein the power management module
comprises a tuning module configured to tune the at least one
functional block of the load circuit according to a given
configuration scheme.
2. The autonomous transducer system according to claim 1, wherein
the power management module further comprises a power budget module
configured to propagate and determine a power budget based on
information of the power supplied by the energy scavenging module
and of power consumed by the at least one functional block.
3. The autonomous transducer system according to claim 2, wherein
the given configuration scheme is at least partly selected based on
the power budget.
4. The autonomous transducer system according to claim 2, wherein
the given functionality of the at least one functional block is
tuned according to the given configuration such that the power
budget is positive.
5. The autonomous transducer system according to claim 2, wherein
the power budget module is configured to determine the power budget
taking the dynamic power consumption and the leakage power of the
at least one functional block into account.
6. The autonomous transducer system according to claim 2, wherein
the power budget module is configured to determine the power budget
taking storage properties of an energy storage module into
account.
7. The autonomous transducer system according to claim 1, wherein
the given configuration scheme is at least partly selected based on
external settings and/or user defined parameters.
8. The autonomous transducer system according to claim 1, wherein
the at least one functional block of the load circuit comprises a
plurality of tunable parameters for setting the given configuration
scheme.
9. The autonomous transducer system according to claim 1, wherein
the power management module further comprises circuitry for
measuring the temporal voltage behavior of the energy storage
module, wherein the temporal voltage behavior is taken into account
in the given configuration scheme.
10. The autonomous transducer system according to claim 1, wherein
the tuning module is configured to tune the given functionality by
adapting the sampling frequency of an analog to digital converter
and/or adapting the frequency of transmission and/or reception.
11. A method of managing the power budget of an autonomous
transducer system, the method comprises: determining a power budget
based on information of power supplied by an energy scavenging
module and of power consumed by at least one functional block of a
load circuit of the transducer system; and tuning the given
functionality of the at least one function block according to a
given configuration such that the power budget is positive.
12. The method of managing the power budget of an autonomous
transducer according to claim 11, wherein the process of tuning the
given functionality comprises adapting the sampling frequency of an
analog to digital converter and/or adapting the frequency of
transmission and/or reception.
13. The method of managing the power budget of an autonomous
transducer according to claim 11, wherein the process of
determining the power budget takes the dynamic power consumption
and the leakage power of the at least one functional block into
account.
14. The method of managing the power budget of an autonomous
transducer according to claim 11, wherein the process of
determining the power budget takes storage properties of an energy
storage module into account.
15. The method of managing the power budget of an autonomous
transducer according to claim 11, wherein the given configuration
scheme is at least partly selected based on the power budget.
16. The method of managing the power budget of an autonomous
transducer according to claim 11, wherein the given configuration
scheme is at least partly selected based on external settings
and/or user defined parameters.
17. The method of managing the power budget of an autonomous
transducer according to claim 11, further comprising measuring the
temporal voltage behavior of an energy storage module, wherein the
given configuration scheme is at least partly selected based on the
temporal voltage behavior.
18. An autonomous transducer system comprising: means for
scavenging energy; means for storing energy; means for providing at
least one functional block; and means for providing power supplied
by the energy scavenging means to the functional block providing
means or for exchanging power with the energy storage means,
wherein the power providing or exchanging means comprises means for
tuning the at least one functional block of the functional block
providing means according to a given configuration scheme.
19. The autonomous transducer system according to claim 18, further
comprising means for measuring the temporal voltage behavior of the
energy storing means, wherein the given configuration scheme is at
least partly selected based on the temporal voltage behavior.
20. The autonomous transducer system according to claim 18, wherein
the power providing or exchanging means further comprises means for
determining a power budget based on information of the power
supplied by the energy scavenging means and of power consumed by
the at least one functional block.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. provisional patent application 61/361,261
filed on Jul. 2, 2010, which application is hereby incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The disclosed technology generally relates to devices having
energy scavenging modules that employ efficient power management
operations.
[0004] 2. Description of the Related Technology
[0005] Low-power consumption and small volume are key demands for
wireless autonomous transducer solutions (WATS) architectures. This
demand is a motivation to work on various advanced miniaturized
energy systems (ES) that can efficiently deliver power to demanding
applications. To enable autonomy these systems need to be
efficiently combined with low-power consumption electronics.
[0006] It is critical to maximize the autonomy, while satisfying
user performance requirements. Commercially available wireless
sensor platforms often rely on general purpose processors and
standard radios, such as ZigBee or Bluetooth radios, which lead to
high power consumption. Typically such applications have power
consumption values in the order of tens of mW in active modes. As a
result, their application is constrained to battery-operated
systems, thus having a limited autonomy. Research efforts for WATS
have been focused on power optimization at block level in the past:
ultra-low power radios, energy harvesters, batteries and power
management circuits. In order to improve the integration efficiency
and achieve increased autonomy WATS architectural modeling becomes
necessary. Previous work on energy management architectures has
been reported in X. Jiang, J. Taneja, J. Ortiz, A. Tavakoli, P.
Dutta, J. Jeong, D. Culler, P. Levis, and S. Shenker, "An
Architecture for Energy Management in Wireless Sensor Networks,"
International Workshop on Wireless Sensor Network Architecture,
Cambridge, Mass., USA, April 2007. The basic idea behind this
architecture is to reduce the overall power consumption, switching
to low-power modes at block level when possible, while satisfying
application constraints.
SUMMARY OF CERTAIN INVENTIVE ASPECTS
[0007] Certain inventive aspects relate to a transducer system with
increased autonomy, and further to a method for managing the power
budget of such a transducer system.
[0008] One inventive aspect relates to an autonomous transducer
system. The system comprises an energy scavenging module, energy
storage module, a load circuit comprising at least one functional
block providing a given functionality and a power management module
arranged for providing power supplied by the energy scavenging
system to the load circuit or for exchanging power with the energy
storage module. The power management module further comprises a
tuning module configured to tune the at least one functional block
of the load circuit according to a given configuration scheme.
[0009] Furthermore, the power management module comprise a budget
module configured to determine a power budget based on information
of the power supplied by the scavenging module and of power
consumed by the functional blocks. In particular, the given
configuration scheme is at least partly selected based on the power
budget.
[0010] In an embodiment the given configuration scheme is at least
partly selected based on external setting means and/or user defined
parameters.
[0011] In an embodiment the at least one functional block of the
load circuit comprises a plurality of tunable parameters for
setting the given configuration scheme.
[0012] In an embodiment the power management module further
comprises circuitry for measuring the temporal voltage behavior of
the energy storage system and wherein the temporal voltage behavior
is taken into account in the given configuration scheme.
[0013] In another aspect a method for managing the power budget of
an autonomous transducer system is presented. The system comprises
an energy scavenging module, an energy storage system, a load
circuit comprising at least one functional block providing a given
functionality and a power management module arranged for providing
power supplied by the energy scavenging system to the load circuit
or for exchanging power with the energy storage. The method
comprises a) determining a power budget based on information of the
power supplied by the scavenging system and of power consumed by
the at least one functional block and b) tuning the given
functionality according to a given configuration such that the
power budget is positive, i.e. the consumed power does not exceed
the supplied power. In several embodiments, the step of tuning can
comprise adapting the sampling frequency of an analog to digital
converter, adapting the frequency of transmission and/or
reception.
[0014] In an embodiment the step of determining a power budget
takes the dynamic power consumption and the leakage power of the
functional blocks into account, for example the dynamic power
consumption and/or leakage power of a microcontroller or the
dynamic power consumption and/or leakage power of sensors.
[0015] In an embodiment the step of determining a power budget
takes storage properties of the energy storage system into account,
for example the state of charge of the energy storage system or the
battery maximum capacitance or the efficiency of power manager.
[0016] A `power generation consumption` diagnosis tool has been
developed. By applying this tool the key power consumers at the
WATS architectural level are identified. In other words, the
average power consumption is substantially continuously compared
with the power generated by the energy scavenging system. The aim
is to learn and to implement optimum power generation-power
consumption (positive power budget). This modeling approach is
effective for improving the WATS autonomy. The system functionality
can be adapted to the application environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Presently preferred embodiments are described below in
conjunction with the appended drawing figures, wherein like
reference numerals refer to like elements in the various figures,
and wherein:
[0018] FIG. 1a and FIG. 1b show autonomous transducer systems
according to one embodiment.
[0019] FIG. 2 shows a plot illustrating the typical power
consumption of a WATS (zoom-in FIG. 3).
[0020] FIG. 3 shows a plot illustrating the typical power
consumption of a WATS (zoom-out FIG. 2).
[0021] FIG. 4 plots a battery charging process whereby the energy
is generated by a photovoltaic harvester device.
[0022] FIG. 5 shows a block diagram of a receiver architecture.
[0023] FIG. 6 shows a plot of the power consumption of an
analog-to-digital converter.
[0024] FIG. 7 illustrates a possible CPU architecture.
[0025] FIG. 8 shows plots illustrating the power trends (a) and
autonomy duration (b,c) with (c) and without (b) an energy
harvester.
[0026] FIG. 9 shows a block scheme of a WATS system with switch
modules (on/off).
[0027] FIG. 10 shows a block scheme of a WATS system with switch
modules between different voltage levels.
[0028] FIG. 11 shows a plot illustrating the degradation of a
number of storage systems.
[0029] FIG. 12 shows a plot illustrating the reversible capacity
loss as a function of the temperature for an energy storage system
(ESS).
[0030] FIG. 13 illustrates the WATS autonomy decrease at lower
temperatures.
[0031] FIG. 14 illustrates the WATS autonomy decrease during ESS
degradation.
[0032] FIG. 15 shows a plot of the impedance of a storage system
measured as a function of (a) aging and (b) temperature.
[0033] FIG. 16 shows a plot of the discharge profiles and voltage
drop of a storage system measured as a function of (a) aging and
(b) temperature.
[0034] FIG. 17 shows a plot of the voltage for an ESS as a function
of the experiment time during different states of the WATS
system.
[0035] FIG. 18 shows plots illustrating the power trends and
autonomy duration with and without an energy harvester.
[0036] FIG. 19 shows a block diagram of a WATS system.
[0037] FIG. 20 illustrates the power consumption trend for a WATS
system.
[0038] FIG. 21 illustrates the autonomy for a WATS system.
[0039] FIG. 22 shows a block diagram of a WATS system.
[0040] FIG. 23 illustrates the power consumption trend for a WATS
system.
[0041] FIG. 24 illustrates the autonomy for a WATS system.
[0042] FIG. 25 illustrates the autonomy for a WATS system.
[0043] FIG. 26 shows a flowchart of one embodiment of a method of
managing the power budget of an autonomous transducer system.
DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS
[0044] The present disclosure will be described with respect to
particular embodiments and with reference to certain drawings but
the disclosure is not limited thereto. The drawings described are
only schematic and are non-limiting. In the drawings, the size of
some of the elements may be exaggerated and not drawn on scale for
illustrative purposes.
[0045] Furthermore, the terms first, second, third and the like in
the description, are used for distinguishing between similar
elements and not necessarily for describing a sequential or
chronological order. The terms are interchangeable under
appropriate circumstances and the embodiments of the disclosure can
operate in other sequences than described or illustrated
herein.
[0046] Moreover, the terms top, bottom, over, under and the like in
the description are used for descriptive purposes and not
necessarily for describing relative positions. The terms so used
are interchangeable under appropriate circumstances and the
embodiments of the disclosure described herein can operate in other
orientations than described or illustrated herein.
[0047] The term "comprising" should not be interpreted as being
restricted to the means listed thereafter; it does not exclude
other elements or steps. It needs to be interpreted as specifying
the presence of the stated features, integers, steps or components
as referred to, but does not preclude the presence or addition of
one or more other features, integers, steps or components, or
groups thereof. Thus, the scope of the expression "a device
comprising means A and B" should not be limited to devices
consisting of only components A and B. It means that with respect
to the present disclosure, the only relevant components of the
device are A and B.
[0048] FIG. 1a shows an autonomous transducer system according to
one embodiment. The system comprises an energy scavenging module,
an energy storage system (ESS), a load circuit comprising one or
more functional blocks or load modules providing a given
functionality and a power management module arranged for providing
energy supplied by the energy scavenging system to the load circuit
and/or for exchanging energy with the ESS. The power management
module further comprises a module for tuning the at least one
functional block of the load circuit according to a given
configuration scheme.
[0049] FIG. 1b shows a more detailed example of an autonomous
transducer system, comprising typical load modules for a wireless
autonomous transducer system (WATS). The power management module
deals with the conversion between the energy system (energy
harvester and storage) and the electronics. The basic task of the
energy scavenger or harvester is to convert ambient energy into
electrical energy. The ESS can be a battery and stores the
irregular energy obtained from the harvester and copes with the
high crest factor (peak/RMS current) of the load current caused by
sensing and/or read-out circuitry, Analog-to-Digital converter
(ADC), microcontroller (.mu.C) and radio. The .mu.C carries out low
level processing of the sensed signal, which the radio can transmit
wirelessly to for example a central processing node.
[0050] In WATS the power budget (P.sub.b) should be larger than or
equal to 0. This is denoted as `autonomy condition` and is given
by
P.sub.b=P.sub.g-P.sub.c>0 Equation 1
where P.sub.g denotes the generated power (typically expressed in
[.mu.W]) and P.sub.c the consumed power (also typically expressed
in [.mu.W]).
[0051] The generated power comprises a contribution of the energy
harvester--energy storage (optional), i.e. battery or
supercapacitor. Examples of energy harvesting technologies are
photovoltaic (PV), thermal, RF and vibrational. The consumed power
is typically the power consumed by the load circuit but also caused
by a contribution of the leakage power. The load circuit comprising
sensing and/or read-out circuitry (for example for sensing a
temperature, for reading out biopotential signals), an ADC (for
example a SAR ADC), a microcontroller and a radio arranged for
wirelessly transmitting or receiving signals (for example
proprietary 2.4 GHz, Zigbee, BAN radio, Impulse radio, UWB).
[0052] The power consumption considered here comprises a
contribution of the standby and active power. The application
transmission (T.sub.Tx) and sampling periods (T.sub.s) are
important factors that influence the impact of the active and
standby power in the total power consumption. To quantify this
impact the current consumption for two WATS systems will be briefly
discussed.
[0053] In a first example, the current consumption measurement for
a WATS system designed with off-the-shelf electronics is shown in
FIG. 2. The WATS system functionality is to perform a temperature
measurement every 5 seconds and wirelessly transmit the
corresponding information every 10 seconds. This type of WATS
systems may be applied in the environmental or industrial
monitoring domains. The measured average current consumption equals
3.4 .mu.A, where more than 95% of this value is represented by the
standby current. This is explained by a longer period of time that
the WATS system spends in the standby state, i.e. 9999 ms, when
compared with the one in active (transmission and sampling) state,
i.e. 1 ms.
[0054] In a second example, the current consumption measurement for
a WATS system is shown in FIG. 3. The WATS system functionality is
to perform an ElectroMyoGram (EMG) measurement every 2 ms and
wirelessly transmit the corresponding information every 140 ms.
This type of WATS system may be applied in body area networks.
Similar with the first example, the contribution of the active and
average current consumption are included in FIG. 3. It follows from
this figure that the average current consumption equals 170 .mu.A,
where more than 95% of the total power is consumed during the
active state. This may be explained by fast repetition of the
T.sub.Tx and T.sub.s.
[0055] In order to enable autonomy PV energy harvesting can be
integrated in this WATS system. In this case, during a `Light-on`
time period the energy generated by the PV harvester is used for
charging a battery and power the WATS system. A power management
circuit may assure proper charging and protection of the battery.
During a `Light-off` time period the WATS system is powered only by
the battery. A second power management circuit may regulate the
battery voltage to the voltage supply needed for powering the WATS
electronic components, i.e. microcontroller, radio,
Analog-to-Digital converter (ADC). It follows from FIG. 4 that the
measured average battery voltage remains constant during the
complete WATS system test. So, the power budget meets the condition
given by Equation 1 and the system is autonomous.
[0056] To obtain information on the power consumption and
generation at system level an architectural power diagnosis tool
has been developed. The tool identifies the key power consumption
blocks at architectural level and quantifies the importance of the
energy harvesting and low-power electronics technologies within a
certain application domain. The application conditions at the
energy harvesting and electronics levels are the inputs for the
power diagnosis tool and determine the given configuration scheme
according to which at least one functional block of the load
circuit can be tuned. For example, the radio reception (Rx) and
transmission (Tx) intervals and the ADC sampling interval are some
of the important input parameters defined within the diagnosis tool
and can also be tuned according to a given configuration scheme.
Another input is the distance range that the application requires.
For a given set of input application parameters the tool selects
the power modes at each described block, i.e. radio, .mu.C, etc.,
so that the overall power consumption at the architectural level is
minimized. For this the tool takes into account transition times
between modes and the input application Tx/Rx intervals. The output
is a diagnosis of the power consumption and autonomy under the
application specific conditions at architectural level. Therefore,
all functional blocks will be discussed below and a solution or a
configuration scheme will be given providing the most, optimal
power budget management. The scheme can also take the properties
and behavior of the ESS into account. The scheme proposes the
settings in the functional blocks. In addition, the configuration
scheme can also be (at least partly) selected based on external
setting modules and/or user defined parameters. Some settings of
functional blocks can be selected by a user (for example user sets
instances of transmission or user can indicate that system may not
work when the power budget is below a predetermined value).
[0057] One of the power consuming blocks of a WATS is for example
the radio. To illustrate that the change of values of different
register parameters in a radio system significantly affects the
radio power consumption (P.sub.radio), a superregenerative receiver
is considered. As shown in FIG. 5, the main block is the radio
frequency (RF) oscillator which periodically starts up and shuts
off oscillation controlled by a quench oscillator. The power
consumption of the quench oscillator depends on its chosen
operating stage (N). The stage is determined by the current in the
digital-to-analog converter (DAC) in the quench oscillator, which
could be pre-controlled in a number of steps. For example, for a
32-step quench oscillator, a 10 .mu.A current consumption
difference is measured between adjacent steps. Measurement results
show that the total current consumption including the low-noise
amplifier (LNA), RF oscillator, quench oscillator and envelop
detector (see FIG. 6) could be ranged from 152 to 462 .mu.A
dependent on the chosen stage in the quench oscillator. This result
means that for a voltage of V power supply (V.sub.dd), the active
power consumption ranges from 182.4 to 554 .mu.W. So, the actual
power consumption of the radio could be estimated by reading the
operating stage register N by
P.sub.radio=V.sub.dd*(152 uA+(N-1)*10 uA) Equation 2
[0058] Another example (i.e. another power consuming block)
illustrates the power consumption of the ADC (P.sub.ADC), which is
determined as a function of the sampling frequency. This power
consumption comes from both the analog and digital part. For the
superregenerative receiver measurement results are shown in FIG. 6
and learn that the power scales linear with the sampling frequency,
down to 6 nW at standby. For a sampling frequency (f) of 10 MHz,
the total power equals 26 .mu.W. Using a least-squares fitting
technique, the following equations are obtained
{ P ADC = 6 .times. 10 - 9 if f < 500 Hz P ADC = 2 .times. 10 -
12 f + 5 .times. 10 - 9 if 500 Hz .ltoreq. f .ltoreq. 5000 Hz P ADC
= 2.57 .times. 10 - 12 f + 2.5 .times. 10 - 8 if f > 5000 Hz
Equation 3 ##EQU00001##
[0059] The power consumption of the microcontroller (.mu.C) is
composed of dynamic (or active) and leakage power consumption. The
active microcontroller power consumption (P.sub..mu.c) may be
determined by
P.sub..mu.C.sup.Dyn=CV.sub.dd.sup.2f.sub.CLK.alpha. Equation 4
where C denotes the design capacitance, V.sub.dd denotes the .mu.C
supply voltage in [V], f.sub.CLK denotes the clock frequency in
[Hz]. .alpha. denotes the average switching activity factor and is
directly related to T.sub.Tx and T.sub.s.
[0060] The .mu.C leakage power consumption is determined by
P.sub..mu.C.sup.L=V.sub.ddI.sub..mu.C.sup.L Equation 5
where I.sub.L denotes the leakage or the OFF state current in
[.mu.A] and may be determined by predefined measurements.
[0061] An example of regular central processing unit (CPU)
architecture is depicted in FIG. 7, where the power modes and their
power consumption at V.sub.dd of 2.2 V are shown in the table
1.
TABLE-US-00001 TABLE 1 Nominal power Power Modes Operation
description Consumption [.mu.W] Active at 1 MHz CPU on, all clocks
active 616 clock LPM3 Only power manager enabled 2 32 KHz clock
LPM4 CPU off (only leakage power) 0.3
[0062] The architecture consists of a CPU core for calculations and
control of its periphery and surroundings. These components
normally operate in an always on mode, which can be high energy
consuming in idle operation. To minimize energy consumption the CPU
Core is able to control the power status of the peripherals and the
core itself. In this way dynamic and leakage power can be
minimized. As an example, when the standby state time period is
much longer than the active time period most of the peripherals and
the CPU can be powered down putting the microcontroller in a sleep
mode. The on-chip power manager would wake-up the relevant
components and/or CPU when an (external) event occurs such as a
timer or signal input. The power modes for the microcontroller can
be programmed by the engineer by setting the control (CTRL)
registers in the power manager.
[0063] The power control of the peripherals targets to minimize
dynamic and leakage power consumption. This may be realized with
clock gating and power gating. Power gating connects a device to a
power supply via a switch and is very suitable for applications
with long standby periods where leakage power is the dominant
factor of the entire power budget (see FIG. 2). Significant power
savings can be made in systems where the leakage power takes 95% or
more of the budget. When a component is power gated the switch is
opened and the device is physically disconnected from the power
supply. This method may have a long duration for powering up and
loss of configuration after powering up the device. This former
requires intelligent control to determine which and what mode to
set, while the latter requires re-programming the configuration
when the device's power is stable.
[0064] A first possible embodiment is to use switches between the
power management and the WATS system loads (see FIG. 9). In this
case, a digital control signal is given by the .mu.C to the system
power management unit. The microcontroller signals to the power
management unit which of the switch modules have to be put in
`Open` or `Close` state. When one of the switch modules is in
`Open` state the corresponding WATS module will be disconnected. As
a result, the component contribution to the standby and leakage
power is eliminated from the total WATS system power
consumption.
[0065] In another possible embodiment the power supply voltage for
each of the WATS components may be actively controlled between two
(or more) voltage levels. The control signal to the power
management module is given by the microcontroller based on
information retrieved from the internal registers (see FIG. 10).
The advantage of such an implementation may be a fast start-up time
of the WATS components. A combination of the two discussed
embodiments is also possible. In both situations the internal power
management registers of the microcontroller can be used to signals
which components have to be put in a specific power mode. The
appropriate mode is determined and set by the CPU core of the
microcontroller.
[0066] Similar to the microcontroller system the power consumed by
the sensing unit in a WATS system is a contribution of the active
(P.sub.sensor) and standby or leakage (P.sub.sensor.sup.L) power.
The equations below describe the power calculation during the
active and standby states
P.sub.sensor=V.sub.ddI.sub.sensor.sup.ON Equation 6
P.sub.sensor.sup.L=V.sub.ddI.sub.sensor.sup.L Equation 7
It may be concluded from the examples above that the WATS system
power consumption may be estimated by combining predefined
measurements with information retrieved from the WATS components
registers.
[0067] Next to the power generated by energy harvesting device, the
properties of the energy storage system also need to be studied.
During usage of wireless autonomous systems the capacity of the
integrated energy storage system (ESS) will degrade, as illustrated
in FIG. 11 wherein the state-of-charge during cycling (SoC.sub.a)
is plotted over time for different types of batteries. The
SoC.sub.a has been calculated each cycle by dividing the measured
ESS capacity to the reference maximum ESS capacity. ESSs have been
always fully charged. After a rest step, a discharge has been
considered until the defined End-of-Discharge level has been
reached. After a rest step a `Deep-Discharge` step at a low C-rate
current has been applied until the defined End-of-Discharge level
has been reached.
[0068] Subsequently, when ESSs are used at low temperatures, e.g.
about -20 to 0.degree. C., the available capacity is much lower
when compared with the ESS capacity available at higher
temperatures, e.g. about 25 to 100.degree. C. FIG. 12 shows the
reversible capacity loss shown by the ESS voltage during discharge
for one ESS as a function of the temperature. The SoC has been
calculated each discharge by dividing the measured ESS capacity to
the reference maximum ESS capacity. ESSs have been always fully
charged. After a rest step, a discharge has been considered until
the End-of-Discharge level has been reached.
[0069] A wireless autonomous system usually operates under various
temperature conditions and at a constant average discharging
current or load over time. As a result, the autonomy of the
wireless autonomous system will decrease at lower temperatures
and/or over time. In FIGS. 13 and 14 a typical example of the WATS
autonomy decrease due to usage during the ESS degradation and at
lower temperatures for two ESSs is illustrated, where the same
result has been confirmed by measuring other ESSs also. Therefore
the wireless autonomous system average discharge current or load
needs to be adapted with the temperature or/and during the energy
storage system aging. This prevents the power consuming parts from
drawing more energy than available in the energy storage system
which enables system autonomy for longer periods of time compared
to a system without adaptive energy usage. It is thereby prevented
that no data is collected and/or transmitted during a certain
amount of time, which might be unacceptable for certain
applications.
[0070] A first possible solution for the adaptation process is to
measure the ESS impedance, see FIG. 15, which decreases with the
temperature and increases with ESS degradation. Another possible
embodiment is to monitor the change in the ESS voltage-drop during
discharging time (see FIG. 16) at the specific discharge current.
In both cases, an increase in the impedance or/and voltage-drop
values with temperature and/or cycling may be used as input for
calculating an optimum discharge average current. A combination of
these two measured parameters is also possible. The decreasing of
the average discharge current may be realized by, for example,
adding an adaptive capacitor filtering network in the WATS system
design. A second possible solution is to reduce the communication
traffic through the WATS with the aged ESS. With this solution,
data will then still be collected continuously, only the time
interval between the readings will increase, but this interval
between charging periods of the energy storage will remain
constant. A third possible solution is to use an adaptive supply
voltage for the WATS loads. The adaption of this voltage supply
will be function of the temperature and ESS aging. In this case a
decrease in the supply voltage with the decrease in the temperature
and/or with the ESS aging will also decrease the average current
and power consumption.
[0071] In another embodiment, the evolution in the voltage of the
energy storage system is measured. An increase or decrease in the
ESS voltage can be used for determining a link between the
generated and consumed power. [0072] An increase in the ESS voltage
shows that the power consumed (P.sub.c) by the WATS loads is higher
than the power generated (P.sub.g) by energy harvesting (see FIG.
17) [0073] A decrease in the ESS voltage value shows that the power
consumed by the WATS loads is lower than the power generated by
energy harvesting (see FIG. 17) [0074] A constant ESS voltage value
shows that the power consumed by the WATS loads equals the power
generated by energy harvesting (see FIG. 17) This relative behavior
will be stored over time. Function of the ESS voltage change, the
functionality of the wireless autonomous system is indicated. In a
first case, when the ESS voltage decreases over time the activity
of the WATS system should be reduced. In a possible embodiment this
can be realized by reducing the application period. In another
possible embodiment the supply voltage of the WATS functional
blocks may be actively decreased. The reduction factor is adapted
as function of the ESS voltage evolution. In a second case, when
the ESS voltage increases over time, an increase in the WATS
activity may be realized without reducing the WATS autonomy. By
combining the two cases an optimal usage of the WATS system may be
found when the ESS voltage remains constant over time.
[0075] In order to predict the autonomy duration, the power
generated by energy harvesting needs also to be estimated. For this
purpose information regarding the increase or decrease in the
battery voltage (see for example FIG. 3) is combined with
information on the battery maximum-capacity and battery
State-of-Charge (SoC) values
P.sub.g=V.sub.av*Q.sub.max*.DELTA.SoC/.DELTA.t Equation 8
where Q.sub.max denotes the battery maximum-capacity in [mAh],
.DELTA.SoC denotes the difference between two SoC values in %
measured in a predefined time difference .DELTA.t in [s] and
V.sub.av denotes the battery average voltage in [V] measured within
this .DELTA.t interval.
[0076] It should be noted that Equation 8 takes also into account a
possible efficiency loss due to the power management circuit
between the harvester and battery. So, only the useful power
generated by the harvester to the battery is taken into account in
the P.sub.g calculation. By replacing Equation 8 into Equation 1
and taking into account the efficiency of the power management
circuit between the battery and the loads (.eta..sub.PM) [%] one
obtains
P b = P g - P c = V bat * Q max * .DELTA. SoC .DELTA. t .eta. PM (
I total , V bat , V dd ) 100 - P c .gtoreq. 0 Equation 9
##EQU00002##
[0077] where V.sub.bat denotes the battery voltage and I.sub.total
denotes the total current consumption over the loads, i.e. radio,
ADC, .mu.C, and sensor, in [.mu.A]. When no power management
circuit is considered between battery and the load then
.eta. PM ( I total , V bat , V dd ) 100 = 1. ##EQU00003##
[0078] In order to meet the condition given by Equation 9 the
P.sub.c value needs to be continuously adapted to the P.sub.g value
generated under the application environment. This adaptation
process may be used for learning and prediction of the most optimum
system usage over time under various application conditions.
Additionally, the battery maximum-capacity and battery life-time
optimization may also be taken into account during the learning and
prediction process.
[0079] During the P.sub.c adaptation process T.sub.Tx and T.sub.s
need to be adapted such that the result obtained by applying
equation 9 is higher than 0.
[0080] It follows from these figures that the autonomy duration is
mainly dependent on [0081] The current consumption during the
standby and active (transmission and sampling) states [0082] The
transmission and sampling periods repetition time [0083] The power
generated by the energy harvester When these variables are
determined by the methods described here the system autonomy is
enabled under any application conditions. In order to integrate the
method described by the equations 2-9 the total number of
operations performed by the microcontroller will increase. In this
case, the active time-period of the microcontroller when
implementing the algorithm
(T.sub..mu.C.sub.--.sub.active.sup.method.sup.--.sup.ID) is higher
than the normal active time-period (T.sub..mu.C.sub.--.sub.active).
This situation is described by
[0083] T .mu. C_active method_ID = T .mu. C_active + N operation
method_ID f CLK .mu. C Equation 10 ##EQU00004##
where N.sub.operations.sup.method.sup.--.sup.ID denotes the number
of operations executed to implement the method operations described
in this ID and f.sub.CLK.sup..mu.C denotes the .mu.C clock
frequency.
[0084] An example of power consumption and autonomy duration
calculation is given in FIG. 18 where T.sub..mu.C.sub.--.sub.active
equals 80 .mu.s, N.sub.operations.sup.method.sup.--.sup.ID (worst
case scenario for solving and implementing the equations given in
this patent) and f.sub.CLK.sup..mu.C equals 5 MHz. So,
T.sub..mu.C.sub.--.sub.active.sup.method.sup.--.sup.ID equals 20
.mu.s. In this example, the adaptation process used for learning
and prediction of the most optimum system usage over time is
performed at every 10 seconds. It follows from FIG. 18 that
implementing the method according to certain embodiments does not
have an impact on the system power consumption and autonomy
duration. So, the system autonomy is enabled without significant
impact on the system power consumption.
Illustrative example
Use of Power Diagnosis Tool for Body Area Networks
[0085] In the context of biomedical applications, different signals
can be measured from the human body, for example EMG and ECG
signals. EMG and ECG are techniques for evaluating and recording
the activation signal of muscles. Table 2 summarizes the EMG and
ECG application specifications at the electronics level.
TABLE-US-00002 TABLE 2 Value Value Application parameter at EMG ECG
the electronics level application application Reception interval
[ms] 1000 1000 Number of bits reception 12 12 [bit] Transmission
interval [ms] 140 35 Number of bits per sample 12 12 (transmission)
[bit] Sampling interval [ms] 2.5 2.5 Transmission/reception 10 10
range [m]
The transmission (reception) interval denotes the time with which
the data packets are transmitted (received). It follows from the
table above that the transmission interval for the EMG application
is lower than that of the ECG application. The impact of this
parameter on the WATS power consumption and autonomy will be
discussed.
[0086] Information about the power generation and consumption of
every WATS block under various conditions have been obtained based
on the manufacturer datasheets, measurement of the power
consumption and generation at block level. For example, the ADC
unit on MSP430F1611 .mu.C has been characterized on the .mu.C
evaluation board as function of sampling frequency and voltage
reference. The ADC power consumption in terms of internal and
external voltage reference of V at sampling intervals of 10 and 100
ms, has been measured. The results are shown in the table 3.
TABLE-US-00003 TABLE 3 Voltage Sampling Average power reference
interval [ms] consumption [.mu.W] Internal 2.5 64 10 27 100 11
External 2.5 50 (2 .mu.W 10 23 consumption) 100 11
It can be concluded from the ADC measurement results that the power
consumption under an external ADC reference is lower in most cases,
especially when the sampling frequency is relatively high.
Furthermore, a stable external ADC reference may also guarantee
higher accuracy during the sampling operation.
A. Power Diagnosis Tool; Results by WATS Architectural Level
Modeling
[0087] The power consumption obtained for a WATS based on
off-the-shelf blocks for an EMG application has been firstly
estimated. The system blocks are illustrated in FIG. 19. The power
management (PM) (32% of total power budget), radio (RF) (26% of
total power budget), sensor and read-out blocks (25% of total power
budget) are the key power consumption blocks. The power consumption
of the RF and ADC blocks (10%) is mainly attributed to the high
power levels consumed by these blocks during the active, i.e. Tx/Rx
and sampling, modes. In order to better understand the impact of
the ADC sampling interval (Ts) [ms] and radio transmission interval
(Ttx) [ms] the WATS power consumption and autonomy are plotted as
function of these parameters in FIG. 20 and FIG. 21, respectively.
It follows from these figures that the power consumption (autonomy)
importantly increases (decreases) at faster sampling and
transmission intervals.
B. Impact of Low-Power Electronics Technology on Power Consumption
and Autonomy
[0088] In a second example, the power diagnosis for an optimized
WATS (see FIG. 22) is shown. The total power consumption of the
WATS system has been reduced to 122 .mu.W. This is explained by a
lower power consumption of the PM (18%), ADC (<1%) and radio
blocks (10%) during the active modes. For comparison, the power
consumption and autonomy under extended transmission and sampling
conditions are plotted in FIGS. 23, 24 and 25. It follows that the
power consumption (autonomy) levels are in most of the cases lower
(higher) for the WATS architecture designed according to the
proposed method.
C. Impact of Energy Harvesting Technology on the Application
Autonomy
[0089] The impact of the energy harvesting on the WATS autonomy is
discussed in this section. In this case, an energy harvester
generating 200 .mu.W of power at 4V and the system illustrated in
FIG. 22 are considered. FIG. 25 illustrates the autonomy as
function of Ts [ms] and Ttx [ms]. It follows from this figure that
an autonomous WATS may be enabled by energy harvesting under
limiting application transmission and sampling intervals.
D. Comparison: EMG Versus ECG BAN Applications
[0090] For comparison the power estimation and autonomy results
obtained under the EMG and ECG application specifications are given
in the table below. It follows from this table that important
improvements have been achieved for both EMG and ECG applications
by implementing energy harvesting and the low-power electronics
technology. As example, a factor of about 17 and 5, respectively,
longer autonomy is enabled under the EMG and ECG, respectively,
application conditions when compared with the architecture designed
with off-the-shelf electronics.
TABLE-US-00004 TABLE 4 Value Value Application parameter at the EMG
ECG electronics level application application Power consumption
(off the 300 480 shelf) [.mu.W] Power consumption (IMEC) 122 164
[.mu.W] Autonomy without energy 130 95 harvesting (off the shelf)
[h] Autonomy with energy 221 134 harvesting (off the shelf) [h]
Autonomy with energy 3694 726 harvesting (IMEC) [h]
[0091] Ultra-low power electronics are integrated with energy
systems, i.e. energy storage and harvesting, within a developed
power generation consumption diagnosis tool for BAN applications. A
comparison is shown for WATS architectures with different choices
of functional blocks, i.e. processor, radio, etc., under realistic
ElectroMyoGram (EMG) and ElectroCardioGram (ECG) monitoring
applications. By applying the power diagnosis tool the key power
consumers at the WATS architectural level are identified. An
optimized system based on the low-power electronics technology is
analyzed. The results show the effectiveness of our modeling
approach for improving the WATS autonomy. Subsequently, the
importance of the energy harvesting and low-power electronics
technology within the BAN application domain is also revealed.
[0092] FIG. 26 shows a flowchart of one embodiment of a method of
managing the power budget of an autonomous transducer system. The
method 200 includes, at a block 210, determining a power budget
based on information of power supplied by an energy scavenging
module and of power consumed by at least one functional block of a
load circuit of the transducer system. The method may further
include, at a block 220, tuning the given functionality of the at
least one function block according to a given configuration such
that the power budget is positive.
[0093] The foregoing embodiments of methods are embodied in the
form of various discrete blocks. In one embodiment, the functions
of any one or more of those blocks may be realized, for example, by
one or more appropriately programmed processors or devices.
[0094] It is to be noted that the processor or processors may be a
general purpose, or a special purpose processor, and may be for
inclusion in a device, e.g., a chip that has other components that
perform other functions. Thus, one or more aspects of the present
invention can be implemented in digital electronic circuitry, or in
computer hardware, firmware, software, or in combinations of them.
Furthermore, aspects of the invention can be implemented in a
computer program product stored in a computer-readable medium for
execution by a programmable processor. Method steps of aspects of
the invention may be performed by a programmable processor
executing instructions to perform functions of those aspects of the
invention, e.g., by operating on input data and generating output
data. Accordingly, the embodiment includes a computer program
product which provides the functionality of any of the methods
described above when executed on a computing device. Further, the
embodiment includes a data carrier such as for example a CD-ROM or
a diskette which stores the computer product in a machine-readable
form and which executes at least one of the methods described above
when executed on a computing device.
[0095] The foregoing description details certain embodiments of the
disclosure. It will be appreciated, however, that no matter how
detailed the foregoing appears in text, the disclosure may be
practiced in many ways. It should be noted that the use of
particular terminology when describing certain features or aspects
of the disclosure should not be taken to imply that the terminology
is being re-defined herein to be restricted to including any
specific characteristics of the features or aspects of the
disclosure with which that terminology is associated.
[0096] While the above detailed description has shown, described,
and pointed out novel features of the disclosure as applied to
various embodiments, it will be understood that various omissions,
substitutions, and changes in the form and details of the device or
process illustrated may be made by those skilled in the technology
without departing from the scope of the disclosure.
* * * * *